What is the boolean value of integers other than 0 or 1?

Question

I was writing a simple function to derive a new filename based on a set of files that should be named as cam1_0.bmp, cam1_1.bmp, and tried this out.

static int suffix = 0;
std::string fPre("cam");
std::ifstream fs;
std::string fName;
do {
    fName = fPre;
    fName.append(std::to_string(camera)).append("_").append(std::to_string(suffix)).append(".bmp");
    fs.open(fName);
} while (fs.good() && ++suffix);

This works and it made me wonder what is the standard, defined behavior of corresponding boolean values for number values other than 0 or 1. With this experiment I know all values including negative values other than 0 evaluates to true. Is only 0 considered to be false as per the standard?

Answer 1

In C++, integers don't have boolean values. (Different languages have different rules, but this question is about C++.)

The result of converting an integer value to type bool (a conversion which is often done implicitly) is well defined. The result of converting 0 to bool is false; the result of converting any non-zero value to bool is true.

The same applies to floating-point values (0.0 converts to false, all other values convert to true) and to pointers (a null pointer converts to false, all non-null pointer values convert to true).